The present invention relates to an illumination circuit, which controls the illumination of an indicator provided in a vehicle interior, and a method for controlling an illumination circuit.
A vehicle includes an indicator, which indicates the vehicle state or an abnormality, and an illumination circuit, which controls the illumination of the indicator. Japanese Laid-Open Patent Publication No. 2004-325324 describes an example of such an illumination circuit. As shown in FIG. 7, an illumination circuit includes a micro-processing unit (MPU) 71, a transistor 72, and an indicator 73. The MPU 71 activates or deactivates the transistor 72 to control the illumination of the indicator 73. The indicator 73 includes a mark 74, which indicates the content of a warning, and a light emitting diode 75. When the transistor 72 is activated, the light emitting diode 75 is lit to illuminate the mark 74. The MPU 71 provides the transistor 72 with a pulse width modulation (PWM) signal based on illumination information or darkening information of the indicator 73, which is obtained by a sensor, to perform pulse width modulation (PWM) control on the light emitting diode 75. When the MPU 71 illuminates or darkens the light emitting diode 75, the MPU 71 changes the duty ratio of the pulse width modulation (PWM) signal to gradually change the brightness of the light emitting diode 75. In this manner, the illumination control generates a fade-in effect, which gradually brightens the light emitting diode 75, or a fade-out effect, which gradually darkens the light emitting diode 75.
In the illumination circuit of Japanese Laid-Open Patent Publication No. 2004-325324, when an ignition switch deactivates the power supply of the vehicle, the MPU 71 stops operating. Thus, the indicator 73 cannot be illuminated. However, it has become desirable that the indicator 73 be illuminate even when the MPU 71 stops operating.
One aspect of the present invention is a vehicle indicator illumination circuit including an indicator that indicates a vehicle state or abnormality. A control circuit is operated by an ignition power supply. The control circuit controls power that is supplied to the indicator. A power supply route extends to the indicator. The power supply route includes a first route that closes when the control circuit operates and a second route that opens when the control circuit operates. When the control circuit stops operating, the first route opens and the second route closes, and the power supply route extending to the indicator is automatically switched from the first route to the second route.